оя угловая конфигурация:

Angular CLI: 1.7.2
Node: 6.10.0
OS: win32 x64
Angular: 5.2.5
... animations, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router

@angular/cli: 1.7.2
@angular-devkit/build-optimizer: 0.3.2
@angular-devkit/core: 0.3.2
@angular-devkit/schematics: 0.3.2
@ngtools/json-schema: 1.2.0
@ngtools/webpack: 1.10.1
@schematics/angular: 0.3.2
@schematics/package-update: 0.3.2
typescript: 2.6.2
webpack: 3.11.0

Мой файл package.json:

{
  "name": "xxxx",
  "version": "0.0.0",
  "license": "MIT",
  "scripts": {
    "ng": "ng",
    "start": "ng serve --proxy-config proxy.conf.json",
    "build": "ng build --prod",
    "test": "ng test",
    "lint": "ng lint",
    "e2e": "ng e2e",
    "ng2ninja": "ng2ninja"
  },
  "private": true,
  "dependencies": {
    "@angular/animations": "5.2.5",
    "@angular/common": "5.2.5",
    "@angular/compiler": "5.2.5",
    "@angular/core": "5.2.5",
    "@angular/forms": "5.2.5",
    "@angular/platform-browser": "5.2.5",
    "@angular/platform-browser-dynamic": "5.2.5",
    "@angular/router": "5.2.5",
    "@ng-bootstrap/ng-bootstrap": "^1.0.0",
    "bootstrap": "4.0.0",
    "core-js": "2.4.1",
    "font-awesome": "4.7.0",
    "rxjs": "5.5.6",
    "tslint-sonarts": "^1.6.0",
    "yarn": "^1.5.1",
    "zone.js": "0.8.19"
  },
  "devDependencies": {
    "@angular/cli": "^1.7.1",
    "@angular/compiler-cli": "5.2.5",
    "@angular/language-service": "5.2.5",
    "@types/jasmine": "2.8.6",
    "@types/jasminewd2": "2.0.3",
    "@types/node": "8.5.2",
    "@ng-bootstrap/ng-bootstrap": "1.0.0",
    "angular-ide": "^0.9.39",
    "codelyzer": "4.1.0",
    "jasmine-core": "2.8.0",
    "jasmine-spec-reporter": "4.2.1",
    "karma": "2.0.0",
    "karma-chrome-launcher": "2.2.0",
    "karma-coverage-istanbul-reporter": "1.3.3",
    "karma-firefox-launcher": "1.1.0",
    "karma-jasmine": "1.1.1",
    "karma-jasmine-html-reporter": "0.2.2",
    "karma-json-reporter": "1.2.1",
    "ng2ninja": "1.0.17",
    "protractor": "5.2.2",
    "ts-node": "4.1.0",
    "tslint": "5.9.1",
    "typescript": "2.6.2"
  }
}

Я получаю это сообщение об ошибке при запуске команды 'ng test' :

 TypeError: this.handler.handle is not a function
            at MergeMapSubscriber.__WEBPACK_IMPORTED_MODULE_2_rxjs_operator_concatMap__.a.call [as project] node_modules/@angular/common/esm2015/http.js:1174:28)
            at MergeMapSubscriber._tryNext node_modules/rxjs/_esm2015/operators/mergeMap.js:109:1)
            at MergeMapSubscriber._next node_modules/rxjs/_esm2015/operators/mergeMap.js:99:1)
            at MergeMapSubscriber.next node_modules/rxjs/_esm2015/Subscriber.js:83:1)
            at ScalarObservable._subscribe node_modules/rxjs/_esm2015/observable/ScalarObservable.js:42:1)
            at ScalarObservable._trySubscribe node_modules/rxjs/_esm2015/Observable.js:171:1)
            at ScalarObservable.subscribe node_modules/rxjs/_esm2015/Observable.js:159:1)
            at MergeMapOperator.call node_modules/rxjs/_esm2015/operators/mergeMap.js:78:1)
            at Observable.subscribe node_modules/rxjs/_esm2015/Observable.js:156:1)

Это мой тест:

import {TestBed, inject} from '@angular/core/testing';
import {HttpClientTestingModule, HttpTestingController} from '@angular/common/http/testing';
import {UserService} from './user.service';
import {environment} from '../environments/environment';
import {JwtInterceptorService} from './jwt-interceptor.service';
import {User} from './services/model/user';
import {HttpClient, HttpHandler} from '@angular/common/http';
...
     it('should authenticate a user', () => {
        // spy on the store method
        spyOn(userService, 'storeLoggedInUser');

        const credentials = {login: 'toto', password: 'titi'};
        let actualUser;
        userService.login(credentials).subscribe(fetchedUser => actualUser = fetchedUser);
    ...
      });

После анализа и отладки проблема возникает из-за вызова метода входа в систему службы пользователя.

Просматривая многочисленные посты (и решения), я не понимаю истинное происхождение моего сообщения об ошибке.

Это мой пользовательский сервис:

 login(credentials): Observable<User> {
    var headers = new HttpHeaders();
    headers.append('Content-Type', 'application/x-www-form-urlencoded');

    var paramCredentials = "grant_type=password"
      + "&credentials=true"
      + "&scope=read write"
      + "&accept=application/json"
      + "&username=" + credentials.username
      + "&password=" + credentials.password;

    return this.http.post<User>(`${environment.oAuthUrl}/oauth/token`, paramCredentials, {headers: headers}).pipe(
      tap(user => this.storeLoggedInUser(user))
    );
  }

 storeLoggedInUser(user) {
    window.localStorage.setItem('jwtToken', JSON.stringify(user));
    this.jwtInterceptorService.setJwtToken(user.token);
  }

Есть идеи ?

Заранее благодарю